Thermoelectric And Electrochromic Properties Of Oligo(Oxyethylene)-Substituted/Bridged Polythiophene

Conducting polymers have unique optoelectronic properties,they have been widely used due to the low price,easy processing,rich colors and other prominent advantages.However,as the deep research and the increasing requirements of the practical performance,developing new structure of conducting polymer materials with excellent characters is quite urgent for the scientific researchers.The special activity of?and?-position in heterocyclic thiophene makes its variable structure,and the introduction of substituent groups can not only improve the solubility of the polymer,but also have a purpose to modify the polymer with specific function,in especial electrical properties to enlarge the practical application of conducting polymers.Researches have shown that cross network has positive effects on the adhesion,mechanical property and stability,which provides a reliable method for assembling electronic devices with high performance.Therefore,we choose thiophene derived with oligo?oxyethylene?as the precursors to prepare novel polymers via electrochemical method,then measure and analyze their electrochemical,thermoelectric and electrochromic properties.The major contents and conclusions are as follows:1.We synthesized the polyether-bridged 2,2-bithiophenes by the Williamson reaction and the Suzuki coupling reaction,and investigated the electrochemical polymerization of as-synthesized monomers in ACN/LiClO₄ solution and the optical,electrochemical and electrochromic properties of the as-prepared P?BT-E-BT?polymers.The increase in conjugation reduced the oxidation potential of BT-E-BT,P?BT-E-BT?exhibited favourable electrochemical activity and thermal stability,and the versatile coloration change for P?BT-E-BT?films on a ITO glass electrode were achieved from salmon pink?neutral state?to blue-green and transmissive rusty red?oxidized states?.Further electrochromic investigation implied that the polymer P?BT-E-BT?films showed moderate to high contrast ratios,good coloration efficiencies up to 372.8 cm² C^-1,low switching voltages,fast response times,especially excellent stabilities and colour persistence as potential electrochromic materials.2.A free-standing copolymer film?P?BT-E5-BT-co-EDOT??based on BT-E5-BT and3,4-ethylenedioxythiophene?EDOT?has been synthesized by electrochemical polymerization.The electrical conductivity of P?BT-E5-BT-co-EDOT?(16 S m^-1)has improved by four orders of magnitude compared to that of the homopolymer P?BT-E5-BT?at room temperature.Spectroelectrochemistry studies indicate that the P?BT-E5-BT-co-EDOT?has a lower band gap in the range of 1.83–1.90 eV,and shows more plentiful electrochromic colours?green,blue,purple and salmon pink?compared with the homopolymer P?BT-E5-BT?.The copolymer of P?BT-E5-BT-co-EDOT?shows the reasonable optical contrast?26%?and satisfied coloration efficiency(205.41 cm² C^-1).The proposed free-standing copolymer provides a direction for fabricating an organic electrochromic device.3.An oligo?oxyethylene?-functionalized thiophene with two EDOT units as building blocks was synthesized via Stille reaction,then comparatively investigated its electrochemical polymerization in three electrolytes,and the free-standing polymer of P?EDT-E5-EDT?was successfully prepared at a low oxidation potential.Interestingly,the solvent is a key factor in the growth process of polymer,one ordered film obtained from PC/LiClO₄ resulted in its electrical conductivity up to 40 S m^-1,and a highest Seebeck coefficient of 35.9?V K^-1 received from the polymer in ACN/LiClO₄.Moreover,the resultant films were demonstrated the electrochromic nature by color changing from salmon pink to blue,and broad absorption can be observed in near infrared region with the band gaps of 1.88–1.93 eV.Further switching transmittance revealed that polymers had reasonable contrast ratios?17.35–52.36%?,high coloration efficiencies(151.6–363.5 cm² C^-1),excellent switching stability and color persistence.These results indicated that the effective EDOT moieties in the chain contributed to the forming of free-standing films as well as their advanced properties.4.We successfully synthesized a series of thiophene derivatives used EDOT unit as building block and oligo?oxyethylene?or alkyl as side chains,systematically studied the electrochemical polymerization of monomers in PC/LiClO₄ solution and the structure-properties of as-prepared polymers.The different electronic nature together with steric hindrance of substituents on the structure resulted in the obviously different optical and thermoelectric properties of corresponding polymers,alkyl groups bearing electronic ability were particularly useful substitutions for the polymers to obtain an ideal electrical conductivity of 1.3×10² S m^-1,meanwhile revealed lower optical band gaps?1.64 eV?as well as reasonable optical contrast?41%?in the visible region.Difference in optical absorption led to neutral electrochromic polymers with multicolors under different applied voltages,and polymers bearing oligo?oxyethylene?showed superior coloration efficiency as high as 361 cm² C^-1.We demonstrate that such polymers are amenable to functionalization depending on the substitutions and interesting in application for electrochromic and thermoelectric materials.